In general, a liquid crystal display device (LCD) comprises a liquid crystal cell and polarizer. The polarizer comprises protective films and a polarizing film, and is obtained by staining a polarizing film made of a polyvinyl alcohol film with iodine, stretching the polarizing film, and laminating protective films on both sides of the polarizing film. In a transmissive liquid crystal display device, this polarizer is mounted on both sides of the liquid crystal cell, and one or more of optical compensation sheets may be also disposed. In a reflective liquid crystal display device, a reflective plate, a liquid crystal cell, one or more optical compensation sheets and a polarizer are disposed in the same order. The liquid crystal cell comprises liquid crystalline molecules, two sheets of substrates to enclose the molecules in between, and an electrode layer to apply voltage to the liquid crystalline molecules. The liquid crystal cell performs ON/OFF display on the basis of the difference in the orientation state of the liquid crystalline molecules, and there have been suggested display modes such as TN (twisted nematic), IPS (in-plane switching), OCB (optically compensatory bend), VA (vertically aligned) and ECB (electrically controlled birefringence), that are applicable both to the transmissive and reflective types.
Among these LCDs, for the uses where high display quality is needed, a 90° twisted nematic liquid crystal display device (hereinbelow, referred to as TN mode) which employs nematic liquid crystal molecules having positive dielectric anisotropy and is operated by a thin film transistor, are mainly used. However, the TN mode shows such viewing angle characteristics that although the devices have excellent display characteristics when viewed from the front, their display characteristics deteriorate when viewed from a tilted direction, in a manner such that the contrast is reduced, or there occurs tone reversal in which brightness is reversed in gray-scale display, or the like. Thus, improvements in these characteristics are highly demanded.
In recent years, as a form of LCD having improvements in such viewing angle characteristics, there has been suggested a vertically aligned nematic liquid crystal display device (hereinbelow, referred to as VA mode), in which nematic liquid crystal molecules having negative dielectric anisotropy are employed such that the longer axes of the liquid crystal molecules are approximately aligned in a vertical direction on the substrate, without any voltage applied, and these liquid crystal molecules are operated by a thin film transistor (See JP-A No. 2-176625). This VA mode shows excellent display characteristics at a level equivalent to the TN mode when viewed from the front, and also exhibits expanded viewing angle characteristics due to the application of a retardation film for viewing angle compensation. It is also known that in the VA mode, even expanded viewing angle characteristics can be realized by using a uniaxially oriented retardation film having positive refractive index anisotropy and a negative uniaxial retardation film having the optical axis in a direction perpendicular to the film plane (See SID 97 DIGEST pp. 845-848)).
However, in such a VA mode liquid crystal display device, if the optical anisotropy of the transparent protective film (also accomplishing the role as a support) holding the retardation films and the polarizing plates is not designed to have an appropriate value, satisfactory viewing angle characteristics cannot be obtained. Furthermore, when the PVA film constituting the polarizing plate contracts under the effect of heat and humidity, stress is exerted on the transparent protective film holding the polarizing plate, whereby a change occurs in the optical anisotropy of the protective film itself. Thus, there have been failures, in particular, deteriorating the display quality of so-called corner spots, which is light leakage at four corners of the screen.
It is known that the corner irregularity is improved by reducing the thickness of a cellulose acylate film used as a protective film of a polarizing plate. However, it is disadvantageous that when the thickness is reduced, retaining a required value of retardation as an optical compensation film becomes difficult.